Signaling Interfaces
Voice ports on routers and access servers physically connect the router, access server, or
call control device to telephony devices such as telephones, fax machines, PBXs, and
PSTN central office (CO) switches through signaling interfaces.
These signaling interfaces generate information about things such as
■ On-hook status
■ Ringing
■ Line seizure
The voice port hardware and software of the router need to be configured to transmit
and receive the same type of signaling being used by the device they are interfacing with
so calls can be exchanged smoothly between a packet network and a circuit-switched
network.
Figure 3-8 Voice Ports
The signaling interfaces discussed in the next sections include FXO, FXS, and E&M,
which are types of analog interfaces. Digital signaling interfaces include T1, E1, and
ISDN. Some digital connections emulate FXO, FXS, and E&M interfaces. It is important
to know which signaling method the telephony side of the connection is using and to
match the router configuration and voice interface hardware to that signaling method.
Voice Port
FXS
(Analog)
T1/E1/ISDN
(Digital)
Serial Port
Telephone to WAN
Telephone to PSTN
IP WAN
Voice Port Serial Port Serial Port Voice Port
V
Voice Port
FXS
(Analog)
E&M
(Analog)
E&M
(Analog)
T1/E1/
ISDN
(Digital)
T1/E1/
ISDN
(Digital)
FXO
(Analog)